Industrial machines, including, but not limited to sheet transport and stacking systems, are often connected to a source of electricity via electrical panels. These panels may have a high-voltage side at which power from the electrical mains arrives. Some of this electricity is distributed to machine components that require high voltage to operate. The remaining current is stepped down to a lower voltage and provided to a low voltage side of the panel. Portions of the machine that operate on a lower voltage receive power from this low voltage side of the panel. The high and low voltage sides of the electrical panel are accessed through separate doors and are physically separated from each other by a wall inside the electrical panel.
A main disconnect panel is generally associated with the main electrical panel of a machine, and this disconnect panel includes a switch for disconnecting power from the main electrical panel and thus from the entire machine controlled by that main electrical panel.
Various safety regulations require that the high-voltage door of an electrical panel remain locked while electrical power is being supplied to the panel. While it may be possible to bypass such a lock with an appropriate key or code, these access routes are only provided to skilled technicians who are assumed to know how to work with high voltage electricity. Otherwise, the lockout mechanism is intended to keep persons from accessing the high-voltage side of the panel while high voltage is present and to keep even skilled persons from accidently accessing the high-voltage side of the panel.
The high-voltage door may be locked by a bolt that slides between a first position that allows the door to open and a second position in which the bolt engages a portion of the door and thus prevents the door from opening. One way to ensure that the high-voltage door of an electrical panel remains locked at all times while current is flowing to the panel is to mechanically connect the lock for the high-voltage door to the main electrical disconnect switch for the electrical panel. When the main disconnect switch is moved from a first position to a second position to break an electrical circuit, a mechanical linkage between the disconnect switch and the bolt moves the bolt from the second position to the first position and unlocks the door. Returning the main disconnect switch to the ON position returns the bolt to the second position locking the high voltage door. Thus a physical movement of the main disconnect switch is required to unlock the high voltage door.
The mechanical linkage between the main disconnect switch and the bolt may be configured such that the bolt can only move back to the second position when the high-voltage door to the main electrical panel is closed. In this manner, the main disconnect switch cannot be shifted to the ON position until the door is closed. In the alternative, it may be necessary to follow certain lock-out procedures, such as applying a padlock to the main disconnect switch, to avoid accidently returning the main disconnect switch to the ON position when the high voltage door is open.
A schematic illustration of a conventional, mechanical, interlock between a switch of a main disconnect panel and a main electrical panel is provided in FIGS. 1 and 2. The main electrical panel is shown in top plan view to better illustrate the movement of the doors, while the main disconnect panel is shown in side elevational view to illustrate the movement of the ON/OFF switch.
The main electrical panel 10 has a high voltage side 12 with a door 14 (sometimes referred to as a “high voltage door” for identification purposes) and a low voltage side 16 with a door 18 (sometimes referred to as a “low voltage door” for identification purposes). A rod 20 is shiftable between a first position, illustrated in FIG. 1, in which the rod passes through an opening 22 in the door 14 of the high voltage side 12 of the electrical panel 10 to prevent the high voltage door 14 from opening. When the rod 20 is shifted to the position illustrated in FIG. 2, the rod 20 no longer passes through the opening 22, and the high voltage door 14 can be opened.
The rod 20 is mechanically connected to an ON/OFF switch 26 of the main disconnect panel 24. When the switch 26 is in the ON position, illustrated in FIG. 1, the rod 20 is held in the first position, locking the high voltage door 14 and preventing the high voltage door 14 from being opened. The switch 20 in the ON position is also shown schematically as holding an electric switch 28 in a closed position to connect a source 29 of electric current to the high voltage side of the main electrical panel 10 via a wire 27.
When the switch 26 is moved to the OFF position, illustrated in FIG. 2, the movement of the switch 26 physically moves the rod 20 to the second position, withdrawing the rod 20 from the opening 22 and allowing the high voltage door 14 to be opened. The switch 20 in the OFF position is also shown schematically opening the electric switch 28 (or allowing a spring-biased switch to spring open) to disconnect the source 29 of electric current from the high voltage side of the main electrical panel 10.
As will further be appreciated from the depiction of FIG. 2, when the high voltage door 14 is open, the rod 20 cannot move through the opening 22 in the high voltage door 14 because the opening 22 is not aligned with the rod 20, and the switch 26 is therefore physically blocked from returning to the ON position until the high voltage door 14 is closed.
A given piece of machinery may include more than one electrical panel similar to the main electrical panel 10. To distinguish these panels, they may be referred to herein as the “main electrical panel” and one or more “subpanels.” Each of the subpanels will have a high voltage side and a low voltage side like the main electrical panel. Each subpanel may also include its own disconnect subpanel which disconnect subpanel includes a mechanical linkage between a disconnect switch and a lock (e.g., a bolt) that secures the high voltage door of the subpanel when current is provided to the particular subpanel. The subpanels can be located on the same machine as the main electrical panel, or, if the main electrical panel is configured to supply electricity to more than one machine, the subpanels can be located on any of the machines supplied by the main electrical panel.
If a person wishes to work on a particular subsystem of a machine, that portion of the machine can be rendered safe by shutting off power at the disconnect subpanel associated with the electrical subpanel that powers the relevant portion of the machine. However, if the main disconnect switch is turned to the OFF position to disconnect power from the main electrical panel and all the subpanels, is still necessary to turn off electrical disconnects at each subpanel because these electrical disconnects also physically coupled to the high voltage doors of each subpanel. It would therefore be desirable to provide a way of simplifying the unlocking of the various electrical panels in a system.